1. Field of the Invention
This invention relates to photosensitive imaging and, more particularly, to producing a radiation-opaque photomask on a photosensitive surface or cover sheet.
2. Description of the Prior Art
It is well known to use a variety of preimaged layers as photomasks for imaging photosensitive elements. Diazo, electrographic, silver halide, and photopolymer films have all been useful for the production of such photomasks. These prior art methods all employ a photosensitive film which is coated or laminated onto a support. After appropriate exposure and processing the photosensitive layer produces density areas comprised of toner, dye, silver, photopolymer, etc. When the photomask layer is placed over a photosensitive element and irradiated, the density areas block or modulate the radiation and thus control the exposure within the photosensitive layer of the photosensitive element.
Both halftone and continuous tone imaging may employ such photomask films or layers. U.S. Pat. No. 3,060,026 teaches that a cover sheet useful for photopolymer films may contain useful information such as graphs or other detail and in this fashion also serve as a photomask layer. U.S. Pat. No. 3,755,892 teaches that a silk-screened image or a developed photosensitive layer may be adhered to the protective layer over a photosensitive resist. U.S. Pat. No. 3,740,225 teaches the use of punched tape as a photomask for imaging a photosensitive material.
Both electrostatic and magnetic toners have been described in useful applications for information transfer. U.S. Pat. No. 2,956,875 discloses toning an electrostatic latent image and transferring the dry powder image to a premoistened gelatine surface to produce a silk screen. U.S. Pat. No. 3,740,205 discloses that magnetic information on a magnetic tape may be toned by a fluid magnetic toner which can then be transferred and fixed upon a surface. U.S. Pat. No. 3,804,511 and U.S. Pat. No. 3,993,484 teach that magnetic toner in correspondence with an electrostatic image may be used to produce surface images by transfer to a copy medium such as paper, to produce multiple or color images. U.S. Pat. No. 4,135,195 discloses magnetic toning which includes a heat transfer step. British patent applications Nos. 2000728 and 2000729 disclose a method of transferring powder magnetic toner via an intermediate magnetized drum to increase resolution of the final image. U.S. Pat. No. 4,117,498 teaches a means for producing colored toner particles suitable for printing on fabric.
A wealth of techniques, devices, and processes are available by which information may be transferred. In the case where it is desired to provide a photomask for the purpose of photoimaging a photosensitive substrate it is necessary to interpose a layer or film between the exposing radiation and the photosensitive substrate. Thus in view of the difficulties attendant with the every increasing demands of productivity it would be advantageous if this process could be simplified so that no layer or film were required.